Electric incandescent lamps having refractory metal phosphate and phosphide coatings for refractory metal leads

ABSTRACT

Lamps operating at high temperatures, and more particularly incandescent or arc lamps having sealed-in lead-in electrical conductors with improved service characteristics and longer service life are fabricated with a &#39;&#39;&#39;&#39;coating&#39;&#39;&#39;&#39;on the aforesaid leads comprising at least one of the following: a phosphate or phosphide of tungsten, or a phosphate or phosphide of molybdenum.

Uited States Patent 11 1 1 3,723,792 Chiola et al. 1 1 Mar. 27, 1973[541 ELECTRIC INCANDESCENT LAMPS [56] References Cited HAVING REFRACTORYMETAL PHOSPHATE AND PHOSPHIDE UNTED STATES PATENTS COATINGS FORREFRACTORY 3,420,944 1/1969 Holcomb 174/1105 METAL LEADS Inventors:Vincent Chiola, 329 York Avenue; James S. Smith, R.D. No. 2; Clarence D.Vanderpool, R.D. No. 2, all of Towanda, Pa. 18848 Filed: Jan. 13, 1972Appl. No.: 217,594

Related U.S. Application Data- Division of Ser. No. 3,937, Jan. 19,1970, which is a continuation-in-part of Ser. No, 647,106, June 19,1967, abandoned.

U.S. Cl. ..3l3/318,174/50.64, 313/315,

1111.0. .1101 j 5/50 Field of Search ..3l3/318, 315, 331, 332; 174/5064Primary Examiner-David Schonberg Assistant Examiner-Paul R. MillerAtt0rney-Norman J. OMalley et al.

[57] ABSTRACT Lamps operating at high temperatures, and moreparticularly incandescent or are lamps having sealed-in lead-inelectrical conductors with improved service characteristics and longerservice life are fabricated with a coatingon the aforesaid leadscomprising at least one of the following: a phosphate or phosphide oftungsten, or a phosphate or phosphide of molybdenum.

11 Claims, 7 Drawing Figures ELECTRIC INCANDESCENT LAMPS HAVINGREFRACTORY METAL PHOSPHATE AND PHOSPHIDE COATINGS FOR REFRACTORY METALLEADS CROSS-REFERENCE TO RELATED APPLICATIONS This application is adivisional application of Ser. No. 3,937, filed Jan. 19, I970, which isa continuation-inpart of our application Ser. No. 647,106, tiled June19, 1967, now abandoned, which is assigned to the assignee of thepresent invention.

BACKGROUND OF THE INVENTION This invention relates broadly to electricaldevices, e.g., lamps, operating at high temperatures; and especially tosuch lamps comprising a sealed bulb or envelope made of a hightemperature-resisting vitreous substance and which contain an electricenergy translation means. The scope of the invention includes bothmethod and article features. The invention further relates to a processfor manufacturing metal phosphides specifically, tungsten, molybdenumand gallium phosphides.

The invention is especially concerned with incandescent or are lampshaving sealed-in leads or lead-ins, i.e., electrical conductors made ofhighly refractory metal that are capable of withstanding the fusiontemperature of the aforesaid vitreous substance, and which are sealed ina highly refractory insulating material, e.g., fused quartz or otherfused silica compositions containing about 95-96 percent, or more, ofsilica. Still more particularly the invention is concerned with thelead-in wire and seal construction of such lamps or other electricaldevices.

Certain incandescent and high-pressure arc lamps operate with very hotenvelopes since they have very high wattage ratings per unit of volume.There has long been a problem in connection with the leads that passthrough the seals of such high-temperature lamps. Socalled quartz-iodinelamps, which are exemplary of improved electrical devices of the instantinvention, typically have molybdenum leads (lead-ins) comprised of amolybdenum foil having fixedly attached thereto a molybdenum wire (orrod) passing through a pressed quartz sea]. In makingsuch lamps thequartz tube is pressed and sealed to the molybdenum foil and wire attemperatures that may reach as high as l,500 C. In lamp-manufacturingpractice, the molybdenum foil and wire are at least partially exposed toair, resulting in formation of molybdenum oxide which, in turn, causesor tends to cause cracking of the quartz and deterioration of the seal.During operation, the temperature reached by the leads as they exit fromthe seals may be as high as 500C. or even higher in some cases. Thus itis seen that the leads are exposed to high temperatures not only duringmanufacture of the lamp but also to a relatively high temperature duringservice use.

In an attempt to solve the problem and to obviate or minimize theabove-described difficulties, platinum rod or platinum-clad molybdenumrods have been used and are still being used in the construction ofleads for lamps operating at high temperatures and/or wherein hightemperatures are encountered during lamp manufacture. However, the highcost of platinum and the difference in its coefficient of linear thermalexpansion as compared with molybdenum (the said coefficient for platinumbeing approximately twice that of molybdenum) have been drawbacks to themore extensive use of platinum or platinum-clad molybdenum rods in thefabrication of leads. Furthermore, the properties of platinum are suchthat it has'certain inherent disadvantages in such applications; for onereason because its use results in higher operating temperatures due toits higher electrical resistivity, and for another reason because of itsrelatively poorer heat-conduction as compared with, for example,molybdenum.

Although pressed quartz seals with sealed-in molybdenum leads forhigh-temperature lamps canbe and are being made, such seals aretroublesome to manufacture in that it is difficult to maintainoxygen-free conditions during manufacture and it is difficult to preventformation of oxides during sealing. Another difficulty arises inobtaining a seal that is bubble-free in the area of the molybdenum foiland rod. The gas bubbles, presumably air, are a potential source ofleaks and/or oxidation (more particularly, oxidation of the molybdenumlead) that eventually lead to a failure of the seal.

Furthermore, the leads operate at such a high temperature during serviceuse of a high-temperature lamp that, unless effectively protectedagainst oxidation, they oxidize slowly. Since molybdenum oxides do notform a protective layer on the leads, the seal deteriorates andeventually fails with the result that the lamp is destroyed.

The phosphides of W, Mo and Ga in particular and refractory metal and/orsemi-conductor phosphides in general are usually prepared by one of thefollowing two methods:

1. The metal powder and phosphors are mixed in various proportions, andheated in evacuated and sealed tubes. Heating times are generally variedbetween 1 hour to 1 month with temperatures between from 550 C. to1,100C. The best results are usually obtained with a uniform temperaturerise from room temperature up to about 800 C. for about 2 days, thencooling to room temperature over a period of about an additional day.

2. Hydrogen phosphine, PH generally obtained from white phosphorus andpotassium hydroxide solution, is dried and passed together with dry,oxygen-free hydrogen, over the desired metal powder which is heated inan electric furnace. Temperatures are maintained between 700-900 C. forabout 2-l0 hours to thereby obtain the metal phosphide.

DISADVANTAGES OF THE OLD METHODS All of the preparations reported in theliterature have at least some of the following disadvantages.

1. Because of the high vapor pressure of phosphorus at elevatedtemperature, explosions of the silica tubes are liable to take place athigh temperatures.

2. The time required for preparation is commercially impractical sinceup to two days time is generally required.

3. PH;,, one of the raw materials in one of the processes, is difficultand hazardous to use on largerthan-laboratory scale.

4. The products generally contain mixtures of monodi and sub-phosphidesand therefore require further purification.

OBJECTS AND SUMMARY OF THE INVENTION It is a primary object of thepresent invention to prothereon an effective and inexpensive protectivecoating (hereafter more fully described and defined) that is easy toapply and/or form in situ.

Another object of the invention is to fabricate such devices wherein theleads are provided with a coating that will strengthen the bond betweenthe refractory metal lead and the refractory vitreous substance, e.g.,fused quartz or silica glass of high silica content.

Still another object of the invention is to provide high-temperatureelectrical devices that have a longer service life as a result of havingsealed-in leads wherein the seal is more resistant to deterioration thanconventional seals employed for this purpose.

A specific object of the invention is to provide a practical, improvedmethod for making tungsten phosphide, molybdenum phosphide and galliumphosphide.

Another object is to provide a commercially feasible process for makingmetal phosphides, particularly refractory metal phosphides andsemiconductor phosphides from oxides.

Another object of the process is to provide the metal phosphides by amethod which by-passes direct reaction of phosphorus and metal underconditions involving long reaction periods, high pressures, sealed tubesand/or high temperatures.

Other objects of the invention will be apparent to those skilled in theart from the following more detailed description and from the appendedclaims.

The objects of the invention are attained by providing the refractory,electrically conducting, metallic leads of electrical devices operatingat high temperatures, especially electrical incandescent lamps havingmolybdenum and/or tungsten leads and connections in wire, rod, foil orother form, with a particular inorganic compound of phosphorus andeither tungsten or molybdenum (i.e., tungsten or molybdenum phosphides);or an inorganic compound of phosphorus, ox-

ygen and either tungsten or molybdenum (i.e., either tungsten ormolybdenum phosphates); or mixtures of the aforesaid inorganic compoundsin any proportions.

The present invention is based on our discovery that coatings ofmolybdenum or tungsten phosphate glasses, as well as molybdenum ortungsten phosphides adhere firmly to surfaces of refractory metals suchas molyb denum and tungsten, e.g., in wire, foil or other form, andprotect them from oxidation in air up'to temperatures of approximately800 C. over long periods of time and up to approximately 1,200" C. forperiods of minutes. In addition, such coatings dissolve the oxides ofmolybdenum and tungsten, thus serving as a flux to create clean,wettable metal surfaces for bonding; and, at the same time, they arecompletely wettable by the silica and silicates of which the lampenvelopesare formed, thereby facilitating the formation of sound pressseals.

We have found that refractory metal and semiconductor metal phosphidescan be produced in essentially pure form by a process comprising forminga solution of the desired metal cation, either in elemental metal formor as the metal oxide, and orthophosphoric acid, H PO heating theresulting solution to form the metal phosphate and to remove the waterpresent and followed by the reduction of the metal phosphate by heat ingin a hydrogen atmosphere under controlled temperature conditions.

BRIEF DESCRIPTION OF THE DRAWINGS The novel features that arecharacteristic of the invention are set forth in the appended claims.The invention will best be understood from the following more detaileddescription especially when considered in connection with theaccompanying drawing wherein FIG. 1 through 6 illustrate somewhatschematically the fabrication of an incandescent lamp wherein theelectrically conducting leads have been sealed in position using theabove-described coating material thereby to obtain one form of theimproved lamp of the invention; and

FIG. 7 is a view of a different form of such a lamp.

DESCRIPTION OF THE PREFERRED EMBODIMENTS known means of making suchlamps in substantially all aspects with the exception of the coating ofthe electrode assembly including the leads. Thus, when it is necessaryto seal a longitudinally supported, extending tungsten filament throughboth ends of a light-transmitting glass envelope and fill the envelopewith an inert gas to retard the vaporization of the tungsten duringsubsequent illumination, one means in common use is essentially asfollows: First the support filament is press-sealed through one end ofthe envelope while the other end is temporarily plugged and while aninert gas is flowing into the envelope. through a centrally appendedexhaust tube. While continuing the flow of inert gas through the exhausttube, the plug is removed, the other end of the envelope is press-sealedand the exhaust tube then tipped off, thus sealing the lamp from theatmosphere and providing a filling of inert gas. The method provides aninert fill gas within the sealed lamp at a pressure of approximately oneatmosphere.

Lamps constituting an embodiment of the instant invention also can befabricated using the technique of the invention disclosed and/or claimedin Gus tin US. Pat. No. 3,162,499 dated Dec/22, 1964, and assigned tothe same assignee as the present invention, and

which by this cross-reference is made a part of the'dis-'.

closure of the instant application.

Referring now to the drawing, wherein the same numbers have been givento the same elements inthe different views, there is shown by way ofillustration in FIG. 1 a perspective view of a sub-assembly,specifically an electrode assembly, 10 comprised of a foil ofrefractory, electrically conducting metal 12, e.g., molybdenum. At oneend of the foil is a lead wire or rod 14 made, for example, ofmolybdenum, which is platinum-brazed to the said foil. A wire or rod 16made,

' vapor-deposition,

- for instance, of tungsten, is similarly fixedly attached by platinumbrazing to the other end of the foil. The larger rod 18 which is rigidlyfastened, e.g., by brazing, to the other end of the lead 14 to form thejoint 20 is used for convenience in handling the work, and may be madeof any suitable metal, e.g., nickel. It'is later cut off from theassembly.

The inorganic phosphorus-containing compounds used in making the sealsfor the leads of the high temperature-operable lamps of this inventionare solids at normal temperatures. They can be volatilized and depositedon the work to-be coated by so-called which is the preferred techniqueemployed in fabricating the quartz-iodine type and other lamps of thisinvention.

FIG. 2 is a view, partly in section, illustrating the application of theinorganic coating material to the electrode assembly shown in FIG. 1.For ease in description, in both this figure and in subsequent figures,tungsten phosphate will be taken as exemplary ofthe.

phosphorus-containing compound employed. The inorganic phosphate (e.g.,tungsten or molybdenum phosphate) may be in the form of a granular solidor in liquid state, e.g., a concentrated syrupy aqueous solution.

Any suitable means for heating the metal phosphate, specificallytungsten phosphate, to its vaporization temperature can be employed.Thus the heating means may take the form of the furnace 22, e.g., anelectric furnace, in which is placed the vessel or boat 24 containingtungsten phosphate 26 in molten state, as shown, at operatingtemperature. The vessel 24 may be constructed of, for example, platinum,fused quartz, high-temperature-resistant silica compositions of highsilica content such as Vycor, and the like. Any suitable support isprovided, e.g., the support indicated at 28, for holding the assembly inthe proper position in the furnace above the molten tungsten phosphateso that the evolved vapors (indicated by the wavy lines) will condenseand be substantially uniformly deposited upon the said assembly. Thetungsten phosphate is conveniently heated in a non-reducing atmosphere,e.g., air, at a temperature within the range of from about 900 C, toabout l,150 C. in order that the desired thin coating will be depositedmost effectively.

FIG. 3 is an enlarged view, partly in section, of a portion of theassembly 10 after it has received the treat ment illustrated in FIG. 2and showing, greatly exaggerated, the solid coating 30 of glassy,phosphorus-containing compound in side section. The composition of thiscoating may be either a refractory metal phosphate or phosphide, or amixture of a phosphate and a phosphide in any proportions, moreparticularly at least one member of the group consisting of tungstenphosphate, tungsten phosphide, molybdenum phosphate and molybdenumphosphide. The phosphides, alone or admixed with the correspondingphosphate, are produced in situ by treating the coated assembly, havingthereon the corresponding phosphate coating, in a reducing atmosphere,e.g., an atmosphere of hydrogen (H at a temperature within the range offrom about 700 C. to about I,l00C.

FIG. 4 illustrates the formation of the seal showing, at one end, theseal of the lamp as having been made and, at the other end, preheatingof the end of the envelope 32 prior to making the seal.

The lamp sub-assembly shown in FIG. 4 is comprised of two of theelectrode assemblies 10 illustrated in FIG. 1 with the leads 16 pointingtoward but spaced from each other and with the intervening coiledfilamentary wire 34 of refractory metal, specifically tungsten,connected to the facing ends of the said leads; or, the leads 16 may beend legs of the coiled wire 34. Any suitable means, e.g., supports 36and 38, can be used to support the sub-assembly for the lamp after ithas been inserted in the envelope 32 prior to press sealing the ends ofthe latter.

In the fabrication of lamps wherein the coiled filamentary wire 34 isconsiderably elongated, for instance several inches or more in length,small spacers of refractory metal, generally tantalum, are positionedabout the'wire along its length to prevent sagging during the life ofthe lamp. When the wire 34 is relatively short or when non-sag wire isused, such spacers may be eliminated as has been done in the case of thefabrication of the lamps illustrated in the drawing of this case.

With further reference to FIG. 4, the burners 40, 42, 44 and 46,together with other similar burners (not shown) if and when required,provide means for heating-the ends of the tubular envelope 32 in orderto soften the fused quartz, high silica glass, or other heat-resistantvitreous substance of which the envelope may be composed, prior topressure-sealing the said ends. The envelope 32 is clamped within clamps(not shown) of a pressure-sealing machine. When the envelope with theafore-mentioned sub-assembly therein is in proper position within thetwo pairs of press sealers 48 and 50 (shown in open position at the leftand in the closed position at the right of FIG. 4) flames from theburners (as illustrated with respect to the flames from burners 40 and42 only) are directed at the open ends of the envelope to soften theglass. When the glass is sufficiently soft, the press sealers are closedand then re-opened in accordance with conventional glass-sealingtechniques. As shown best in FIGS. 5 and 6, when the press seals aremade the pressure-sealing machine forms the raised edges 54 and 56,andthe depressed sections 58 and 60.

Filling of the envelope with an inert fill gas is effected in knownmanner, for instance as briefly described hereinbefore or as disclosedin the aforementioned Gustin US. Pat. No. 3,162,499. After filling, theexhaust tube is sealed, as is illustrated at 52 in FIG. 5 wherein theexhaust tube is shown as having been tipped off, thus sealing the lampfrom the atmosphere and providing a filling of inert gas. Examples ofinert fill gases that are suitable for use in the hightemperatureoperable lamps of the kind with which this invention isconcerned are argon, helium, neon, xenon and krypton; also, certainother gases that are inert or non-reactive with the filament orassociated metal parts, e.g., nitrogen. Gasified halogens, e.g., iodine,bromine, or mixtures of iodine (or bromine) and nitrogen, also can beused.

Referring again to FIGS. 5 and 6, these figures show a lamp, which hasbeen fabricated as hereinbefore described with reference to FIGS. 1through 4, provided at its end with tubular, end-cap connectors 62 and64 through which leads 14 pass to terminals 66 and 68 for connectionwith a source of electrical energy.

The end-cap connectors 62 and 64 can be formed of any of a wide varietyof electrically insulating materials that can be molded, have adequatemechanical strength in molded form, and which are capable ofwithstanding temperatures above 500 C. for prolonged periods of timewithout deterioration. Hence, mainly because of thesetemperature-resisting requirements, inorganic insulators are normallyemployed. Examples of such insulating materials are the various ceramic,electrically insulating substances such as thoria, magnesia, zirconia,beryllia, alumina, silica and titania, combinations of the foregoing invarying proportions; and ceramic materials in which heat-resistingoxides such as the foregoing predominate and which otherwise meet thephysical and electrically insulating requirements in the electricaldevices with which this invention is concerned.

Referring particularly to FIG. 6, which is a sectional view taken alongthe line indicated at 6-6 in FIG. 5, it will be noted that theconnectors 62 and 64 are slotted to form the slots 70 and 72 into whichthe ends of the depressed sections 58 and 60 of the lamp are,respectively, fitted. The fit is made so that the leads 14 pass throughthe central opening in each of the aforesaid connectors to the terminals66 and 68. The connectors are fixedly sealed in position by any suitablemeans. For example, the insulated connectors 62 and 64 can be cementedto the depressed sections 58 and 60 of the pressed seal using a liquidporcelain cement, more particularly Sauereisen liquid porcelain cement,as the bonding agent. The sauereisen cement is applied to the surface ofeither the insulated member or the pressed seal member at the area ofbonding, and the members are fitted together. Bonding is completed byforce-drying the assembly at a temperature of about 150 F. for a periodof up to 24 hours, followedby baking at a temperature up to about 300 C.or higherv to obtain thorough drying and hardening of the cement.

FIG. 7 is illustrative of another type of high-temperature lamp that canbe made with leads sealed in position in accordance with the presentinvention. It is comprised of a bulb or envelope 74 having a sealedexhaust tube 76 at one end and a press-sealed opposite through thesolution, heated successively for 15 minutes first at 400 C. and then atl,000 C. The wire is then used for leads in incandescent lamps of thekind with which this invention is concerned. Tungsten phosphate glassescan similarly be made containing other ratios of tungsten to phosphorus,for example, W:P atom ratios of from 1:5.9 to 1:9. Optimum results areusually obtained when the W:P atom ratio is within the range of from 1:7to 1:8, and still more particularly a W:P atom ratio of 117.6.

end that forms the seal 78. This seal is made in essentially the samemanner hereinbefore described with reference to the sealing of oneof theends of the lamp illustrated in FIGS. 4, 5 and 6. The materials ofconstruction of the electrode assembly and the prior coating of the saidassembly with a tungsten or molybdenum phosphate or phosphide are thesame as have been broadly and specifically described hereinbefore withreference to the other figures of the drawing.

For example, the electrode assembly shown in FIG. 7 includes themolybdenum foils. 80 and 82. At the lower end of the seal and extendingthrough said seal to an end-cap connector (not shown) are the molybdenumleads 84 and 86, which are platinum brazed to the aforesaid foils.Platinum brazed to the other ends of the individual foils are thetungsten wires or rods 88 and 90. Each end of the helically coiledfilamentary wire 92 positioned within the envelope 74 is fixedlyattached to the wires 88 and 90; or the latter may be end legs of coiledwire 92 having a diameter and stiffness such as will provide support forthe said coiled wire, especially after the seal 78 has been made.

. The invention is, of course, not limited to coating of the parts to becoated by vapor deposition of the in the preceding paragraph using, forexample, molybdenum phosphate glasses wherein the atom ratios of MozPare within the range of from 1:5 to 1:10. Wires, foils and the like alsocan be coated by vapor deposition with molybdenum phosphate by passingthe refractory metal to be coated over the hot, molten molybdenumphosphate glass at 1,000 C. In this way a thin coating is applied to themetal. Thin coatings are preferred in order to provide a coating havingoptimum adhesion and flexibility, and from a cost standpoint.

Furthermore, it is not necessary that the phosphoruscontainingcompounds, specifically tungsten phosphate and molybdenum phosphate, beseparately prepared prior to application to the refractory material tobe coated. For example, such phosphates can be prepared directly on themetal, i.e., in situ, by exposing the respective meta], viz., tungstenor molybdenum, to the vapors of P 0 generated when orthophosphoric acidand/or metaphosphoric acid is heated to temperatures within the range offrom about 700 C. to about l,000 C.

The improvement attained by the incandescent lamps of this inventionover lamps which are otherwise the same with the exception that theconductor leads are not coated in accordance with the present inventionis exemplified by the following comparative results:

Quartz-iodine lamps (400 watt, volt) were constructed in accordance withthe general procedure hereinbefore described, using (A) untreated, un-

coated, molybdenum electrode assemblies; (13).

-, platinum-clad molybdenum electrode assemblies; and (C) tungstenphosphate-coated molybdenum electrode assemblies. The temperature of theelectrode assemblies during operation ranged from 500 to 600 C. On lifetesting, the uncoated assemblies (A) failed through oxidation andsubsequent disintegration, with accompanying seal and lamp failure, at100 hours operation. The platinum-clad electrode assemblies (B) failedat approximately hours of life. The tungsten phosphate-coated electrodeassemblies were still on the life test after 200 hours of operation.

It will be understood by those skilled in the art that the presentinvention is not limited to the fabrication of the specific lampsdescribed herein and in the accompanying drawing, or to those lamps,modified in accordance with this invention, that are described in GustinU.S. Pat. No.' 3,162,499 to which crossreference previously has beenmade. For example, lamps embodying the instant invention can be made bythe general procedure otherwise described in such prior-art patents as,for example, U.S. Pat. Nos. 2,667,595; 2,883,571; 3,211,511; 3,211,950,3,259,778; and 3,170,081.

The coating materials employed in making the improved lamps of theinstant invention as a result of the improved seals that are obtainedalso may be used in making various other seals between a ceramic orceramic-like material (including high-melting glass and glass-like)materials on the one hand and metals, especially refractory metals suchas tungsten, molybdenum and alloys of tungsten and of molybdenum, on theother hand. Such seals may be made and form an essential and criticalpart of various electrical and other devices used in commercialindustry, and in aviation, aerospace and other applications. Thus, thephosphorus-containing materials used in practicing this invention may beemployed in making seals, for coatings and in other uses where the partsto be sealed, coated or otherwise modified are exposed to temperaturesas high as about 1,500 C. for a brief period of time during sealing,coating or the like, and which are subjected to operating temperaturesof the order of 500 C. or somewhat above for a longer period of time.

The terms coating, coating, coating material and coated as usedhereinbefore and/or in the appended claims with reference to at leastone substance of the group (A) consisting of tungsten phosphate,tungsten phosphide, molybdenum phosphate and molybdenum phosphide areused both generically and specifically herein. When the aforementionedterms are used specifically the common or dictionary definitions ofthese WOI'dS,Ol' as they are ordinarily understood bythose skilled inthe surface-covering, surface-protective and related arts, is intended.

When employed generically the aforementioned terms include within theirmeanings not only the common or dictionary definitions of these words,or as they are ordinarily understood by those skilled in thesurface-covering, surface-protectiveand related arts, but theyalsoinclude the uniform or non-uniform, regular or irregular stratum orstrata, or other arrangement, of

any solid material that results (e.g., due to heat, pressure, both heatand pressure, or other effect agents or means), separately orconcurrently, from one or more or all of the following:

a. decomposition or degradation of the chosen member(s) of the aforesaidgroup A;

b. interaction between different decomposition or degradation productsresulting from (a);

c. reaction between individual members of the aforesaid group A when twoor more such members are initially present;

d. reaction of. the chosen member(s) of the aforesaid group A with,and/or diffusion into, the material or materials (e.g., refractorymetals, ceramics, glasses including fused quartz, and the like) to beprotectively covered or bonded, joined or sealed together; and

e. reaction of the products resulting from (a), (b) and/or (c) with,and/or diffusion into, the material or materials to be protectivelycovered or bonded, joined or sealed together.

The aforementioned terms (including their derivatives and grammaticalvariations) are used and have been defined generically herein becausethe applicants are presently unable to state with certainty the exactphysical and/or chemical reactions that take place in the course of theformation of (a) the ultimate surface material developed on a substrateor (b) the ultimate sealing component in a bond between two adjacentmaterials, e.g., between molybdenum or tungsten and fused quartz. Inview of the high temperatures involved in manufacturing lamps of thekind with which this invention is concerned, for instance when scalingin the lead-in conductors within the sealed end or ends of alight-transmitting envelope of fused quartz or the like,

it is entirely possible and in some cases probable that one or more ofthe actions set forth in (a) through (e), supra, in the precedingparagraph occur when a tungsten or molybdenum phosphate or phosphide, ora plurality thereof, comprises or constitutes the starting materialemployed in effecting the desired seal or in protectively surfacing arefractory metal or other substrate.

As previously mentioned the metal phosphides are prepared by a processwherein a orthophosphoric acid and an appropriate metal source is formedand is thereafter heated under controlled conditions to form thecorresponding metalphosphate and the phosphate is further reduced to thephosphide by reduction under a hydrogen atmosphere under controlledtemperature conditions.

Although, in general, all refractory metal phosphides and semiconductormetal phosphides can be prepared by the process of this invention,tungsten and molybdenum phosphides and gallium phosphides are thepreferred products. The source of these metals can be the elementalmetals or their respective oxides. Orthophosphoric acid has the formula11 1 0,, and in pure form is a solid that melts at about 39 C to form asyrupy liquid. In most instances, pure H PO will not be used and acidscontaining from about percent to about 98 percent by weight arepreferred. Lower concentrations tend to contain excessive water that hasto be removed, therefore, are not generally preferred. Higherconcentration, that is, above 98 percent H PO can be used; however,viscosity problems can result, therefore, are not used with standardequipment.

After the solution of orthophosphoric acid and the appropriate metalsource is formed, the solution is heated to drive off the water that ispresent or is formed from the reactions between the metal source and theacid. Heating is continued at elevated temperatures, that is, up toabout 900 C to insure all the metal source has been converted to metalphosphate. Generally, about 30 minutes at 900 C is sufficient to insureconversion to the metal phosphate that are solids.

The solid phosphates are thereafter heated at temperatures of betweenabout 700 C to about l,l00 C for at least about 3 hours and under ahydrogen atmosphere thereby reducing the phosphates to phosphides. Thematerials thus produced are pure phosphides, as determined by X-ray andchemical analysis.

solution of i To more fully illustrate the process of this inventionwherein metal phosphides are produced the following detailed examplesare presented. All parts, proportions and percentages are by weightunless otherwise indicated.

EXAMPLE 1 About 1.8 parts of tungstic acid is mixed with 4.9 parts ofphosphoric acid 98 percent, in a suitable container. The slurry isheated slowly with agitation and with an accompanying loss of wateruntil the temperature reaches about 520550 C. Care is exercised toprevent the solution from boiling over until a temperature of about 400C has been reached. At this temperature the reaction becomes mild. Thetemperature is then increased to about 900 C and held for about 30minutes. This completes the dissolution of oxide and the formation ofmetal phosphate. The deep blue liquid is poured, while still hot, onto acold surface where it solidifies. After cooling the glassy tungstenphosphate is crushed. The product is typically an amorphous compositionsof W and P 0 The crushed tungsten phosphate is heated in a tube furnaceto about 700-900 C while hydrogen at a flow of about 8-10 cu. ft./hr. ispassed over it. The reaction stops in about 3 hours, and the furnace iscooled while allowing the hydrogen to continue flowing. After cooling toroom temperature, a black powdered product is recovered. The blackmaterial is identified by X-ray analysis as pure tungsten phosphide.Actual chemical analysis shows that the product contains about 85.12% Wand 14.19%,P. The theoretical value .for tungsten phosphide is about85.62% W and 14.37% P.

EXAMPLE 2 EXAMPLE 3 About 1 part of gallium is dissolved in about partsof 85 percent orthophosphoric acid. The solution is heated slowly toabout 100 C until all reactivity had stopped. During the heating, about12 parts of H PO is added to prevent the formation of a heavy syrupthough a loss of H 0. On continued heating a white precipitate is formedin the solution. After cooling to about 40 C resulting solution isdiluted with about 100 parts of water. The white precipitate is removedby filtration and washed with water. After drying, the washed solid istransferred to a silica boat and reduced in a tube furnace with ahydrogen flow as in Example 1. After about 3 hours at 900 C an orangepowder remains in the boat. The material is allowed to cool under a flowof hydrogen. The material turned yellow. The color change of thematerial is reversible at about 50 C. When the material is heated toabout 50 to about 500 C, it is orange and below about 50 C it is yellow.The material is identified by X-ray diffraction as gallium phosphide.

While there has been shown and described what is at present consideredthe preferred embodiment of the invention, it will be obvious to thoseskilled in the art that 2 an incandescible filament of a coiled,electrical v conductor within the said envelope; and 3. electricallyconducting leads sealed within the sealed end or ends of the saidenvelope, v said lead's extending beyond both ends of the seal and beingconnected at one end to the aforesaid filament, and at the other end toa terminal adapted for connection with a source of electrical energy,

and said leads having thereon a coating comprising at least onesubstance of the group consisting of tungsten phosphate, tungstenphosphide,molybdenum phosphate and molybdenum phosphide. 2. An electricincandescent lamp as in claim 1 wherein the incandescible filament of(2) is coiled tungsten filament; and the electrically conducting leadsof (3) are formed of at least onemember of the group consisting oftungsten and molybdenum and wherein said high'temperat'ure resistingvitreous substance is fused quartz.

3. An electric incandescent lamp as in claim 2 wherein the coating on.the electrically conducting leads comprises tungsten phosphate.

4. An electric incandescent lamp as in claim 3 wherein the tungstenphosphate, at least as initially applied has a W:P atom ratio of from125.9 to 1:9.

5. An electric incandescent lamp as in claim 2 wherein the coating onthe electrically conducting leads comprises molybdenum phosphate.

6. An electric incandescent lamp as in claim 5 wherein the molybdenumphosphate, at least as initially applied, has an Mo:P atom ratio offrom1:5 to 1:10.

7. An electric incandescent lamp as in claim 2 wherein the coating onthe electrically conducting leads comprises tungsten phosphide.

8. An electric incandescent lamp as in claim 2 wherein the coating ontheelectrically conducting leads comprises molybdenum phosphide.

9. An electric incandescent lamp ,as in claim 1 wherein the hightemperature-resisting substance of g which the envelope of (l) is formedis fused quartz; the incandescible filament of (2) is coiledtungsten'filament; the electrically conducting lead to which said coiledfilament is'joined at one end is tungsten wire, which latter is joinedat its other end to molybdenum foil; and the lead to the terminaladapted for connection with a source of electrical energy is molybdenumwire, which is joined at one endto the said molybdenum foil and attheother to said terminal.

10. An electric incandescent lamp as in claim 9 wherein the coating onthe said leads and foil is tungsten phosphate wherein the atom ratio, atleast as the said coating is initially applied, is from 1:7 to 1:8.

Patent No. 3,723,792 Dated March 27 1973 lnvenmw VINCENTCHIOLA, JAMES s.SMITH, CLARENCE D.VANDERPOOL It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown-below:

Please add the following to the front page:

[73] Assignee: Sylvania Electric Products Inc.

Signed; and sealed this 13th day" of Novemlj'er 1973.

, (SEAL) Attest: I

EDWARQM. FLETgI-IERJR. Q RENE D. TEGTMEYE R I Attestlng Offlcer ActingCommissioner of Patents Po-wso UNITED STATES PATENT oTTIcE CER'UFICATEOF CURREUHUN Patent No. 3,723,792 Dated March 27 1973 Invent'ms) VINCENTCHIOLA, JAMES S. SMITH, CLARENCE D.VANDERPO1 It is certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:

Please add the following to the front page:

[73] Assignee: Sylvania Electric Products Inc.

Signed and sealed this lSth day' of November 1973.

, (SEAL) Attest:

EDWARD M FLETQI-IE11,JR RENE D TEGTMEYDR I Attestlng Offlcer ActingCommissioner of Patent

2. An electric incandescent lamp as in claim 1 wherein the incandesciblefilament of (2) is coiled tungsten filament; and the electricallyconducting leads of (3) are formed of at least one member of the groupconsisting of tungsten and molybdenum and wherein said high temperatureresisting vitreous substance is fused quartz.
 2. an incandesciblefilament of a coiled, electrical conductor within the said envelope; and3. electrically conducting leads sealed within the sealed end or ends ofthe said envelope, said leads extending beyond both ends of the seal andbeing connected at one end to the aforesaid filament, and at the otherend to a terminal adapted for connection with a source of electricalenergy, and said leads having thereon a coating comprising at least onesubstance of the group consisting of tungsten phosphate, tungstenphosphide, molybdenum phosphate and molybdenum phosphide.
 3. An electricincandescent lamp as in claim 2 wherein the coating on the electricallyconducting leads comprises tungsten phosphate.
 4. An electricincandescent Lamp as in claim 3 wherein the tungsten phosphate, at leastas initially applied has a W:P atom ratio of from 1:5.9 to 1:9.
 5. Anelectric incandescent lamp as in claim 2 wherein the coating on theelectrically conducting leads comprises molybdenum phosphate.
 6. Anelectric incandescent lamp as in claim 5 wherein the molybdenumphosphate, at least as initially applied, has an Mo:P atom ratio of from1:5 to 1:10.
 7. An electric incandescent lamp as in claim 2 wherein thecoating on the electrically conducting leads comprises tungstenphosphide.
 8. An electric incandescent lamp as in claim 2 wherein thecoating on the electrically conducting leads comprises molybdenumphosphide.
 9. An electric incandescent lamp as in claim 1 wherein thehigh temperature-resisting substance of which the envelope of (1) isformed is fused quartz; the incandescible filament of (2) is coiledtungsten filament; the electrically conducting lead to which said coiledfilament is joined at one end is tungsten wire, which latter is joinedat its other end to molybdenum foil; and the lead to the terminaladapted for connection with a source of electrical energy is molybdenumwire, which is joined at one end to the said molybdenum foil and at theother to said terminal.
 10. An electric incandescent lamp as in claim 9wherein the coating on the said leads and foil is tungsten phosphatewherein the atom ratio, at least as the said coating is initiallyapplied, is from 1:7 to 1:8.
 11. An electric incandescent lamp as inclaim 10 wherein the tungsten phosphate, at least as initially applied,has a W:P atom ratio of 1:7.6.